1. Field of the Invention
This invention relates generally to improved disinfecting and/or preserving systems. More specifically, the invention pertains to the use of such systems in solutions for contact lenses and contact lens care.
2. Description of Related Art
Generally, contact lenses in wide use fall into two categories: the hard or rigid corneal type lenses formed from materials prepared by polymerization of acrylic esters, such as polymethyl methacrylate (PMMA), and gel, hydrogel or soft type lenses made of polymerized hydrophilic or hydrophobic monomers, such as 2-hydroxyethyl methacrylate (HEMA). The hard acrylic type contact lenses are characterized by low water vapor diffusion constants, resistance to the effects of light, oxygen and hydrolysis and absorb only minor amounts of aqueous fluids. Because of the durability of hard contact lenses, coupled with their tendency not to absorb appreciable amounts of water, the selection of suitable disinfecting agents, cleaning agents or other lens care compounds is relatively non-critical.
However, unlike hard lenses, soft type contact lenses and certain of the newer gas permeable hard contact lenses have a tendency to bind and concentrate significantly more fluids, environmental pollutants, water impurities as well as antimicrobial agents and other active ingredients commonly found in lens care solutions. In most instances, the low levels of the ingredients in lens care solutions do not lead to eye tissue irritation when used properly. Nevertheless, because of the inherent binding action of protein deposits and soft lens materials disinfecting agents and preservatives tend to build up on lens surfaces and become concentrated to potentially hazardous levels, such that when released can cause corneal inflammation and other eye tissue irritation.
Previous efforts to alleviate the problem of binding and concentrating disinfectants and preservatives onto contact lens surfaces, and reducing the potential for eye tissue irritation have not been totally satisfactory. For example, in spite of low toxicity levels not all disinfectants are compatible for use with all types of contact lenses. Many hard lens disinfecting and preservative solutions contain benzalkonium chloride or chlorobutanol. Although they are effective antibacterial agents, their use can result in a loss of lens hydrophilic properties, cause soluton instability or may even lack compatibility with certain types of hard lenses, e.g., high silicon content.
Other antibacterial agents were found to be more compatible with contact lenses and exhibit less binding on lens surfaces. In one case, it was found that chlorhexidine, a biguanide, binds to soft lens material seven times less than benzalkonium chloride, but the presence of proteinaceous oily tear-film deposits can double the amount of chlorhexidine absorbed over that of clean tissue. U.S. Pat. No. 4,354,952 discloses very dilute disinfecting and cleaning solutions containing chlorhexidine or its salts in combination with certain amphoteric and non-ionic surfactants. These solutions were found to reduce the amount of binding of chlorhexidine on hydrophilic soft contact lenses. Notwithstanding the reduction in finding achieved by this invention, the use of chlorhexidine did result in certain tradeoffs. That is, the antimicrobial activity of the chlorhexidine may be diminished when used with certain amphoteric surfactants. Furthermore, if not used in proper ratio, the surfactant and disinfectant will precipitate unless a non-ionic type surfactant is also employed.
U.S. Pat. No. 4,361,548 discloses a contact lens disinfectant and preservative containing dilute aqueous solutions of a polymer; namely, dimethyldiallylammonium chloride (DMDAAC) having molecular weights ranging from about 10,000 to 1,000,000. Amounts of DMDAAC homopolymer as low as 0.00001 percent by weight may be employed when an enhancer, such as thimerosal, sorbic acid or phenylmercuric salt is used therewith. Although lens binding and concomitant eye tissue irritation with DMDAAC were reduced, it was found in some users to be above desirable clinical levels.
British Pat. No. 1,432,345 disclosed contact lens disinfecting compositions containing a polymeric biguanide (of the type contemplated by applicants) and a phosphate buffer. The concentration of the disinfecting polymer disclosed by this patent is substantially higher than that of the present invention. The products embraced by this patent have not found acceptance by the consumer. Corneal staining is a indication of patient acceptability and compositions as disclosed by this patent have staining value of 17% or more present, far above that which is desirable for patient acceptability, see Table V in the Examples of this application.
Other efforts to reduce or eliminate soft lens binding have led to the use of anti-binding or detoxifying agents, like polyvinyl pyrrolidone (PVP) and polyvinyl alcohol (PVA). However, these polymers alone were found to be ineffective, for the most part, in reducing lens binding and eye tissue irritation.
Accordingly, there is a need for improved disinfecting and preservative solutions which are compatible for use with most types of contact lenses while maintaining both a high level of antibacterial activity and low order of toxicity to eye tissue with little or no binding or concentrating of the disinfecting agent onto lens surfaces.
Accordingly, there is a need for improved preservative systems that maintain a low order of toxicity and irritation to tissue in and surrounding the eye, i.e., the eye itself, the upper eyelid, the lower eyelid, etc.
The present invention provides for improved solutions for disinfecting and/or preserving contact lenses. The solutions are compatible with both hard and soft type lenses, and are adaptable for use with virtually any of the commonly known disinfecting techniques, including "cold" soaking under ambient temperature conditions, as well as with high temperature disinfecting methods. The disinfecting and preservative solutions of the present invention are especially noteworthy for their wide spectrum of bactericidal and fungicidal activity at low concentrations coupled with very low toxicity and reduced affinity for binding and concentrating when used with soft type contact lenses.
In addition to solutions for contact lenses, the instant invention provides for improved preservative systems for cosmetic products, specifically intended for those products used near the eyes. The advantage to this preservative system is its wide spectrum of bactericidal and fungicidal activity at low concentrations coupled with very low toxicity and irritation.